The present invention relates to apparatus for the transfer of relatively flat objects from a first to a second work station and, more particularly, to an air assist means that facilitates such transfer. The present invention is especially adapted for use within equipment for the manufacture of shells used to close the ends of metal cans.
One common way of packaging liquids, particularly beverages such as beer, soft drinks, juices and the like, is within cans typically formed from aluminum. In such cans, the can body is either manufactured to include both the can side walls and an attached bottom end, or the bottom end is formed separately and subsequently joined to the side walls. The upper end, which includes the means by which the can is opened, is manufactured separately and attached to the can body after the can has been filled.
The can ends, often referred to within the art as shells, are generally manufactured within ram presses. While various particular methods of shell formation are known and available, it is often necessary within these methods to transfer the shells from a first to a succeeding work station. In view of the large quantities of cans and shells that are manufactured, it is desirable to be able to form quantites of the shells very rapidly. This necessitates a transfer system that is both quick and reliable.
Various types of transfer systems for shells are known. In one approach, the shell is partially formed within the first tooling station and then positioned for transfer. A device is actuated to strike the shell with an edgewise blow that propels the shell outwardly from the tooling. The shell moves lateraly along a transfer path either out of the press for further processing, or arrives at a second station for additional operations.
An example of this type of transfer system may be seen in U.S. patent application Ser. No. 571,051, filed Jan. 16, 1984. There, a driver extends an actuator to provide the blow for moving the shell along the transfer path. Ideally, the shell moves in free flight without contacting the restraining structure defining the path until the shell is captured at the second station. Of course, any contact by the shell with the surrounding structure, for example as the result of unintentional variations in shell flight direction, will tend to slow the movement of the shell.
This system has been found to be quite reliable. However, particularly where a shall is being transferred into a second work station within the same press, speed and consistency in transfer times is of great importance. While it might be possible to provide detectors for determining the occasional late arrival of shells at the second station, there is no practical way of delaying operations in the station since such operations are under the control of the press drive. With the press typically running at speeds of at least several hundred strokes per minute, the timing of individual strokes cannot be altered. Thus, a late arriving shell could be subjected to forming or other work steps prior to proper positioning within the tooling. At best, this will result in a deformed work piece, but could also cause disruption of the manufacturing process requiring restarting of the press, lodged workpieces, or even damage to the press tooling itself.
A second example may be seen by reference to U.S. Pat. No. 4,554,814 issued to Grow et al. The shell is again struck with a physical blow to move it from the tooling. In this example, however, the shell is struck with a blow insufficient to move the shell the full distance along the path, and as the shell is propelled, it passes along a transfer surface. As part of the surface, a conduit is provided extending along the path and supplied with air under pressure. A series of slots or openings along the length of the path permit the air to emerge under pressure in a direction both upwardly and along the path so that the shell is conveyed along the path by the air emerging from the conduit.
The apparatus disclosed in Grow et al can be advantageous in that the initial impact need not be relied upon for the entire transfer movement of the shell. On the other hand, the transfer apparatus does not operate as quickly. Since the press and associated first station tooling cannot begin its next stroke until the shell has completely cleared the tooling, a longer time period is required between press strokes, thereby reducing the running speed of the press. Further, the conduit must be carefully formed and positioned within the tooling, thereby increasing the cost of the press.
It can be seen, therefore, that any improvement in the transfer mechanism for moving shells from a press tooling and directing them into a transfer path is advantageous. This is particularly the case where such improvements increase either speed or reliability of the transfer process.